The present invention relates to the field of aerial propellers, and more particularly to a propeller blade pivot.
In the present context, the term “aerial propeller” is used broadly to cover any device having at least one profiled blade suitable for rotating about a propulsion axis in order to accelerate a mass of air along the direction of said propulsion axis so as to generate thrust in the opposite direction by reaction. The term thus covers, amongst other things, conventional aviation propellers, and also turbojet fans, including unducted or open rotor fans. Typically, such unducted fans comprise two contrarotating variable-pitch propellers.
Typically, a variable-pitch propeller includes a pivot at the base of each blade to enable the blade to turn about its longitudinal axis. The pivot may be incorporated in the root of the blade or it may be detachable from the blade, thereby making it easier to replace blades and helping to reduce repair and maintenance costs.
Ideally, variable-pitch propellers include devices that act automatically to enable them to be feathered in the event of the engine stopping. In particular, when the blades are feathered, the relative wind can still exert an aerodynamic torque on each blade about its longitudinal axis. In order to oppose that aerodynamic torque and keep the blades in a feathered orientation, one of the simplest devices known to the person skilled in the art comprises a flyweight at the end of a lever arm that extends laterally relative to said longitudinal axis, and perpendicularly to the pressure and/or suction faces of the blade. The centrifugal force exerted on each flyweight by the propeller rotating serves to maintain the blade in the feathered orientation. In order to limit their size, such flyweights and lever arms are typically incorporated in the pivot of each blade. French patent FR 2 957 329 discloses an unducted fan turbojet having two contrarotating propellers in which the pivot of each blade has a device of that type for holding the blades in the feathered position.
Aerial propellers, and more particularly unducted fan propellers that are normally driven by free turbines of the turbojet, can rotate at speeds that are very high, thereby generating large traction forces on the pivots. The pivots are typically made of metal and they are dimensioned to withstand such loads, and consequently they are of considerable weight.